Rationale: Intracellular redox balance is believed critical to maintaining normal functioning of cells of all types, including regulation of cell cycle progression, proliferation, and response to cytotoxic challenges. Aberrations in redox state have implications for a variety of fields, including aging and cancer progression. One mechanism through which redox state determines stress response is through intracellular signaling. Cysteine amino acid residues present in many peptide chains contain sulfhydryl bonds which behave as redox "switches." These "switches," and the proteins they compose, are activated or suppressed depending on oxidative stimuli, including glucose deprivation, hydrogen peroxide exposure, chemotherapeutic agents treatment, and ionizing radiation (IR) exposure. We investigated the effect of redox signaling factor modulation on the tumor cellular response to oxidative stressors. Research Synopsis: As glycolytic metabolism is essential to maintaining cell function and involves electron transport, we investigated the redox component of this process. Altering glycolysis with a glucose mimetic, 2-deoxy-D-glucose (2DG), in HeLa cells instilled sensitivity to IR, an effect that was reversed by pretreatment with a free radical scavenger, N-acetyl-cyteine (Cancer Res 63: 3413-3417). This result reaffirms the role of electron transfer and redox state in metabolism and cytotoxicity. Additionally, we have recently re-inspected our results involving heat-induced radiosensitization in light of a potential for redox modulation of intracellular pathways. In this case also, heat and radiation appear to instill a unique response to both modalities when administered in close temporal proximity that likely has a large redox component (Mattson et al, accepted for publication). As a corollary of these observations, we attempted to modulate the function of additional redox-responsive elements in tumor cells. When thioredoxin reductase (TR) is activated by redox imbalance, it is able to reduce and activate its client protein, thioredoxin (TRX), which in turn activates redox-sensitive signaling machinery, including AP-1 and NF-kB (Cancer Res 60: 6688-6695 and Oncogene 21: 6317-6327). Additionally, we found differences in transcription factor activation based on genetic and pharmacological models of affecting TR activity. Transcription factor modulation correlates with a variety of physiological effects, include cell cycle progression, apoptosis, necrosis, and oxidative stress survival (Ortiz et al, in preparation). Redox-sensitive signaling pathways, including TR and TRX, may therefore represent viable therapeutic molecular targets for interventional therapy that could enhance the tumor response to oxidative damage.